A general drainage ditch refers to a passage for collecting and draining large volumes of sewage. Here, sewage refers to rainwater containing sewage. A discharge side of the drainage ditch is usually connected to a river.
As conventionally known in the art, such a drainage ditch is provided, at the discharge side thereof, with an intercepting sewer, which guides sewage, introduced from the drainage ditch, into a sewage treatment plant for the purification of sewage. The drainage ditch is also provided, in the rear of the intercepting sewer, with a barrier wall structure having a predetermined height. The barrier wall structure serves to prevent soil contained in sewage from entering the intercepting sewer and to filter other wastes.
The intercepting sewer is transversely arranged underneath a longitudinal drainage ditch, and has an upper opening that is formed at the bottom of the drainage ditch to extend throughout the width of the drainage ditch. The upper opening is sectionalized by use of a plurality of longitudinal bars, and a plurality of intercepting plates is arranged by a predetermined distance. Thereby, a plurality of sewage inflow holes, each being defined at opposite sides thereof by the longitudinal bars, is formed between the intercepting plates.
The barrier wall structure includes a plurality of walls to prevent an inflow of soil, and screens interposed between the walls to allow other wastes contained in sewage, except for soil, to be introduced into the intercepting sewer.
The conventional drainage ditch having the above configuration, however, has a problem in that, when an inflow amount of sewage excessively increases due to rainfall, soil flows over the barrier wall structure, and enters the intercepting sewer. As a result, the soil is accumulated in the intercepting sewer, resulting in a reduction in an available drainage cross section of the intercepting sewer. Also, soil, introduced into a sewage treatment plant, degrades purification efficiency of the sewage treatment plant.
To solve the above problems, there are known various conventional soil inflow prevention apparatuses for preventing soil from entering an intercepting sewer when it rains. Hereinafter, several examples of the conventional soil inflow prevention apparatuses will be explained.
Firstly, there is known a soil inflow prevention apparatus (hereinafter, referred to as “a conventional first soil inflow prevention apparatus) as disclosed in Registered Korean Utility Model Application No. 1999-18530.
The conventional first soil inflow prevention apparatus comprises: a frame plate rotatably coupled to one of sewage inflow holes, which are defined at the top of an intercepting sewer, by use of a rear fixing shaft, to open and close the sewage inflow hole; a sewage inlet perforated at the frame plate; a support arranged in the intercepting sewer beneath the sewage inlet; a spring device interposed between a front portion of the frame plate and the support; and a sewage inflow prevention plate mounted beneath the frame plate and adapted to close the sewage inlet when the frame plate closes the sewage inflow hole.
Under normal conditions, the front portion of the frame plate is inclined upward by use of elastic repulsive force of the spring device, so that sewage passes through the sewage inlet, located at the downwardly inclined rear portion of the frame plate, by a constant flow rate, so as to be guided into a sewage treatment plant by way of the intercepting sewer. However, if an inflow amount of sewage excessively increases due to rainfall, the frame plate is lowered to keep a horizontal state and the sewage inlet is closed by the horizontal frame plate. Thereby, the conventional first soil inflow prevention apparatus having the above configuration allows soil, contained in rainwater, to be directly discharged to a river, without entering the intercepting sewer.
In the case of the conventional first soil inflow prevention apparatus, the frame plate is designed to be opened and closed by use of elastic repulsive force of the spring device. However, this configuration has a problem in that the soil inflow prevention apparatus malfunctions when the spring device losses a restoration force after extended use.
Also, since the spring device is arranged in the intercepting sewer and inevitably always comes into contact with sewage, there is a problem in that the spring device is easily rusted within a short time.
As a solution of the above problems, there is also known a soil inflow prevention apparatus (hereinafter, referred to as a conventional second soil inflow prevention apparatus) as disclosed in Registered Korean Utility Model Application No. 2001-1706.
The conventional second soil inflow prevention apparatus comprises: a support formed at the periphery of a sewage inflow hole of an intercepting sewer; and a frame plate located at a front location of the support to be inclined about a pivoting shaft.
In the conventional second soil inflow prevention apparatus having the above configuration, under normal conditions, the frame plate is inclined so that a rear portion thereof is lowered. Thereby, sewage can be introduced into the intercepting sewer by a constant flow rate, and can be guided into a sewage treatment plant. However, if an inflow amount of sewage excessively increases due to rainfall, a front portion of the frame plate is downwardly pushed until the frame plate is kept in a horizontal state. As a result, soil, contained in rainwater, is directly discharged to a river, without entering the intercepting sewer.
As clearly shown in FIG. 12, where a flow rate of sewage is constant, the frame plate 30 of the conventional second soil inflow prevention apparatus is inclined about the pivoting shaft 20 to open a rear region of the sewage inflow hole, as indicated by a solid line.
However, if an inflow amount of sewage increases due to rainfall, an excess of sewage collides with a lowered portion of the frame plate 20 and is rapidly introduced into the intercepting sewer 10. Thus, the frame plate 30 is rapidly rotated to keep a substantially vertical state, as indicated by a dash dot dotted line.
After the intercepting sewer is completely filled with the sewage, an excess of sewage acts to push a raised portion of the frame plate 30 as it flows over the sewage inflow hole. As a result, the frame plate 30 is kept in a horizontal state after the lapse of a certain time from a time point when the amount of sewage increases, thereby serving to close the sewage inflow hole.
A problem of this configuration is that soil enters the intercepting sewer 10 along with sewage in the beginning of an inflow of sewage.